On the induced charge density distribution in streaming plasmas

Motivated by experiments on the generation of streaming plasmas in high energy density facilities, industrial setups, and fundamental dusty plasma research, the plasma polarization around a test charge in streaming plasmas is considered in this work. The induced charge density distribution of the plasma constituents is discussed for the subsonic, sonic, and supersonic regime taking into account the non- Maxwellian distribution of the flowing ions. It is shown that the plasma polarization (the plasma wakefield) in the vicinity of the test charge shows different scaling in the subsonic and supersonic regimes, where Mach number is defined as the ratio of the ion streaming velocity and the ion sound speed. In contrast to the wake potential, the density decays strongly monotonically in the plasma wake and does not exhibit an oscillatory pattern or trailing maxima. Therefore, the picture of an ion focusing effect creating a separated ion region downstream was not confirmed.